The present invention relates to a color cathode-ray tube with deflection yoke having a magnet device for adjusting the static convergence and purity of a color cathode-ray tube by using external magnetization.
Adjustment of static convergence refers to performing adjustment so that three electron beams ejected from electron guns arranged in order of red (R), green (G) and blue (B) may overlap each other on one point at the center of the cathode-ray tube.
Adjustment of purity refers to performing adjustment so that the spot of an electron beam passed through a shadow mask may lie upon a pixel of a fluorescent luminous body with as small discrepancy as possible.
In order to absorb errors in components and fabrication nonuniformity, a magnet device for adjusting the static convergence and the purity at the central portion of the screen is mounted on a color cathode-ray tube.
As described in JP-B-51-45936 filed on June 10, 1972 by RCA Corporation, for example, a conventional magnet device comprises a plurality of magnet rings magnetized beforehand to have two, four or six poles and rotatably mounted around the neck portion of the color cathode-ray tube. These magnet rings are rotated for adjustment.
However, this structure has a very large number of components. Further, respective magnet rings must be magnetized with high precision, resulting in a high costs. Further, it is necessary to rely upon a highly skilled worker for adjustment. Adjustment in a short time is extremely difficult.
As methods for eliminating such problems, therefore, there were proposed in U.S. Pat. Nos. 3,725,831, 4,138,628, 4,159,456 and 4,162,470, for example, methods comprising the steps of wrapping a barium ferrite sheet directly around the neck section, fixing the barium ferrite sheet directly around the neck section, fixing the barium ferrite sheet by using a tie band or the like, applying magnetization with predetermined controlled strength to a plurality of locations on the above described barium ferrite sheet, and magnetizing the multiple poles so as to generate a magnetic field for realizing predetermined correction.
The above described prior art has problems described below. Since the barium ferrite sheet is used as the magnet member for magnetization, a change in magnetic flux density depending upon temperature is as large as approximately -0.2%/.degree. C. The characteristics change as the temperature of the neck section and the cabinet rises. The static convergence drift is large. In addition, it is difficult to hold the temperature characteristics with high precision which is needed in case fine characters are displayed.
Therefore, it is necessary to use a magnet material having excellent temperature characteristics such as rear-earth cobalt or Fe--Cr--Co. When such a magnet material is used, however, it is difficult to obtain a flexible sheet like material and an integrated structure unlike when a conventional magnet material is used. Even if an integrated structure is used, it is difficult to obtain magnetic field distribution because the permeability of the material is high. On the basis of these facts, it is necessary to dispose a plurality of independent pole pieces around the neck section and adjust the static convergence and purity characteristics by adjusting the amount of magnetization.
Further, the deflection yoke is conventionally fixed by inserting a wedge between the external periphery of funnel of the cathode-ray tube and the inside of the deflection yoke.
As literature relating to such a fixed structure, JP-A-51-55224 (U) filed on Oct. 25, 1974 by Tokyo Shibaura Electric Co., Ltd., IP-A-52-33215 (U) filed on Aug. 29, 1975 by Denki Onkyoh Co., Ltd., JP-A-52-68118 (U) filed on Nov. 17, 1975 by Denki Onkyoh Co., Ltd., JP-A-52-88517 (U) filed on Dec. 14, 1975 by Denki Onkyoh Co., Ltd., and JP-A-53-144620 filed on May 23, 1977 by Mitsubishi Electric Corporation, can be mentioned.
Such a method of inserting a wedge has problems that deviation of the position of the deflection yoke occurs when the wedge is inserted and faulty adjustment of convergence and purity occurs.